1. Field of the Invention
The present invention relates to the field of voice communications over different types of communications networks. More specifically, the present invention relates to an apparatus which interfaces a wireless IP network and a wide area network or public switched telephone network (PSTN) for voice communications.
2. The Background Art
Public switched telephone networks have been used for many years for voice communication. The typical telephone converts sound waves into analog signals, which are then transmitted through the public switched telephone network to another telephone, which converts the analog audio signals back into sound waves. In recent years, wireless and cellular telephones have been rising in popularity, due to their mobility. Users are no longer tied to a stationary telephone, but are free to carry their telephones with them.
With the advent of computers and fax machines, there arose a need to transmit data in a similar fashion. Due to the fact that analog telephone lines were already in existence in every part of the nation, these lines were also used in the transmission of data. Specific protocols were designed, such as the V.32 protocol, which specified how digital data is encoded into analog signals for transmission over public switched telephone networks.
The apparatus that performs conversion from digital data to an analog telephone signal is known as an analog modem. Analog modems do not require dedicated or specialized lines, as they use pre-existing telephone lines, which are already in existence in nearly every home in the country. The main drawback, however, is in the relatively low speed of transmissions. Current protocols allow only up to about 56 Kbps to be transmitted through an analog phone line, and FCC regulations currently limit this number to 53 Kbps due to power output concerns.
Users who require faster transmission speeds have turned to carriers which allow digital transmission, which not only provide much faster speeds and higher bandwidth, but also reduce errors that occur during transmission. Examples of such carriers are ISDN lines, T1 and T3 lines, and cable lines. ISDN lines are in actuality twisted pair telephone lines. While ISDN service allows a user to obtain digital transmission without a dedicated or specialized line, the inherent physical drawbacks of twisted pair lines limits the amount of bandwidth and speed of such systems. T1 and T3 lines are specialized, dedicated lines (T1 lines can carry up to 1.544 Mbps while T3 lines can carry up to 44.736 Mbps.
Cable modems interface to coaxial cable lines that are typically used for providing cable television signals into homes and they provide a large amount of bandwidth. While it is generally necessary for the cable provider to upgrade the overall cable network system in order to enable Internet access through cable modems, it is generally not necessary to install new lines into homes.
Wide Area Networks (WANS) using wireless data communications techniques and systems have been generally available for many years. Implementations exist which employ microwave radio-frequency (RF) communication systems and frequency-modulated (FM) radio communications. The data rate is generally up to 19.2 Kbps, which is sufficient for the intended class of applications. Frequency-modulated communication techniques include both conventional point-to-point radio and broadcast. These systems include RAM Mobile Data Service using the Mobitex protocol; the Advanced Radio Data Information Service (ARDIS), manufactured by ARDIS Company, Lincolnshire, Ill.; and the Cellular Digital Packet Data (CDPD) service.
The ARDIS system, for example, uses a dedicated radio network which includes a number of radio base stations deployed throughout larger metropolitan areas in the United States. The remote devices in the field communicated with the base stations, and vice versa. The base stations are fixed and can cover an approximate radius of 15 to 20 miles when transmitting and receiving. The base stations communicate with a limited number of radio network controllers located at various points throughout the United States. Each radio network controller is responsible for maintaining authorization and registration of the remote terminals. The radio network controllers are further connected to one of three network hubs. The network hubs are connected by dedicated leased lines and are accessed by the customer host applications to send and receive data to and from the remote devices. The customer host applications are also connected to the network hubs by dedicated leased line or through a value added network (VAN).
Wireless local area networks (LANs) are used in business applications such as inventory, price verification mark-down, portable point of sale, order entry, shipping, receiving and package tracking. Wireless local area networks use infrared or radio frequency communications channels to communicate between portable or mobile computer units and stationary access points or base stations. These access points are in turn connected by a wired or wireless communication channel to a network infrastructure which connects groups of access points together to form a local area network, including, optionally, one or more host computer systems.
Wireless infrared and radio frequency (RF) protocols are known which support the logical interconnection of portable roaming terminals having a variety of types of communication capabilities to host computers. The logical interconnections are based upon an infrastructure in which at least some each of the remote terminals are capable of communicating with at least two of the access points when located within a predetermined range therefrom, each terminal unit being normally associated with and in communication with a single one of such access points. Based on the overall spatial layout, response time, and loading requirements of the network, different networking schemes and communication protocols have been designed so as to most efficiently regulate the association of the mobile unit with specific access points, and the availability of the communication channel to individual mobile units for broadcasting.
One such protocol is described in U.S. Pat. Nos. 5,029,183; 5,142,550; 5,280,498; and 5,668,803 each assigned to Symbol Technologies, Inc. and incorporated herein by reference.
Another such protocol is described in U.S. Pat. No. 5,673,031. Still another protocol is set forth in the IEEE Standard 802.11 entitled “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications” available from the IEEE Standards Department, Piscataway, N.J. (hereinafter the “IEEE 802.11 Standard”).
The IEEE 802.11 Standard permits either infrared or RF communications, at 1 Mbps and 2 Mbps data rates, a medium access technique similar to carrier sense multiple access/collision avoidance (CSMA/CA), a power-save mode particularly important for battery-operated mobile units, seamless roaming in a full cellular network, high throughput operation, diverse antennae systems designed to eliminate “dead spots”, and an easy interface to existing network infrastructures.
The basic specifications for the communications of audio, video and multimedia that are applicable to the networks pertaining to the present invention are set forth in the International Telecommunications Union Telecommunication Standards Sect (ITU-T) standards H.320-323.
The H.321 recommendation relates to asynchronous transfer mode (ATM) channels, H.322 to guaranteed Quality of Service LANs, and H.323 to packet based systems. Data packets are created from a compressed data stream of digital voice samples. The data packets are formatted for transmission over a data network. Since network latency and packet transmission delays can be disastrous to the intelligibility and quality of real-time phone conversations, a variety of approaches of giving priority of voice packets (or other real-time multimedia packets) over data packets in the network have been proposed, thus allowing delay-sensitive packets to supercede data packets across any network node in any traffic situation. The H.323 recommendation also provides for call establishment and control, including determining the sequencing and timing of establishing and disconnect procedures, as well as the control of the H.323 session after it is established.
To the extent the Internet Protocol or “IP” (as set forth in IETF RFC 791) is used as the network layer protocol, the recommendations of the International Multimedia Teleconferencing Consortium's Voice over IP Forum are also applicable to such a Voice over IP (“VoIP”) network. In a VoIP network, the voice signal is digitized, encapsulated into IP packets, and then routed between VoIP capable devices in an IP network. These packets of voice may then be delivered in real time as voice communications, or stored as voice mail.
Communications between a LAN and a wide area network or public switched telephone network are generally performed by communications controller known as a gateway. In the H.323 standard, a gateway generally refers to an endpoint which provides for real-time, two-way communications between H.323 terminals on an IP network and other ITU terminals, telephones on a PSTN, and terminals on other networks. An example of a gateway is the Cisco 3600 series of Cisco Systems, Inc. The Cisco 3600 series is a modular gateway that can be configured to provide gateway functions over a wide variety of communications mediums. These include, among others, analog modem access, ISDN access, digital modem access, and voice and fax access. Other types of interfaces between wired LANs and connected or switched networks such as frame relay and ATM networks are known. For example, the ATM Forum has developed a bridging implementation agreement called LAN Emulation (LANE). LANE relies on a LAN Emulation Server (LES), which performs MAC-to-ATM address resolution; a Broadcast and Unknown Server (BUS), which performs data broadcast; and an optional LAN Emulation Configuration Server (LECS), which performs initialization and configuration.
Prior to the present invention, there has not been a simple and user-transparent way to interface a wireless LAN with the diverse range of currently available public and private networks, including the public switched telephone network (PTSN), cable networks, wide area networks (WAN), cellular telephone networks, and satellite communications networks.